4 GEOLOGY OF OHIO. 



the first volume of the Geology of Ohio, great additions have been made 

 to our knowledge of the forms of life contained in these rocks, through 

 the contributions of Messrs. Meek, Hall, Whitfield, and Nicholson. These 

 are contained in Vols. I and II of the Palaeontology of Ohio, in which the 

 descriptions of species occupy 382 pages, and are illustrated by twenty 

 plates. For the means of making this important contribution to palae- 

 ontological science, the Survey is greatly indebted to Messrs. C. B. Dyer, 

 U. P. James, S. A. Miller, D. H. Shaffer, and Drs. Miller, Hill, and Byrnes, 

 all of whom generously placed their splendid collections of fossils in the 

 hands of the palaeontologists mentioned, for description. More new ma- 

 terial is constantly being obtained from this vast storehouse of ancient 

 life, and it is hoped that some of the species discovered since the publi- 

 cation of the second volume on Palajontology, will be described in the 

 third and last volume, which is now in preparation. 



Perhaps the most interesting fossils recently discovered in the Cincin- 

 nati group, are numbers of minute dental organs, collected about Cin- 

 cinnati, by Professor Wetherby and Mr. E. 0. Ulrich. Their zoological 

 relations have not yet been accurately determined : they have much 

 resemblance to the jaws and teeth of fishes, but are perhaps still more 

 like, in form and microscopic structure, the teeth of annelids. Although 

 at first supposed to be fish-teeth, it is much more probable that they 

 formed the dentition of mollusks or articulates; at least, much stronger 

 proof than they afford will be required, before the existence of verte- 

 brates in the Lower Silurian Sea can be conceded. 



UPPER SILURIAN SYSTEM. 



THE MEDINA GROUP. 



Nothing new has been learned since the publication of our first vol- 

 ume, in regard to the existence, in Ohio, of representatives of the Medina 

 sandstone. Deep borings in the northern and central parts of the State 

 indicate the presence there of a stratum of red, mechanical sediment be- 

 tween the limestones of the Cincinnati group and those of the Upper 

 ' Silurian, and there is little doubt that this represents the Medina sand- 

 stone of New York. In south-western Ohio, a sheet of calcareous, colored 

 clays occupies the same position. Professor P. H. Bradley reports that 

 in Indiana the fossils of the Cincinnati Group extend up through this 

 band to the base of the Clinton. We have, however, found this not to 

 be the case in Ohio, nor has any evidence been gathered here which is 

 inconsistent with the supposition that these clays form the extreme 

 edge of the Medina. This is rendered the more probable by the great 



